This invention relates in general to power producing engines and, more specifically, to a high efficiency fluid power engine.
Reciprocating engines using expandable gases, such as steam, to drive the pistons have long been used for a variety of purposes. In such engines, individual charges of steam enter the cylinder space, expand against a piston, and are exhausted, this cycle repeating itself at regular intervals. During this cycle the work output is developed due to the difference of pressure on the two sides of the piston working within the cylinder. These differences of pressure vary widely throughout the stroke of the piston and since the reciprocating motion characteristic of the engine must be changed into a rotation for ready utilization of its power output, the design of the engine must usually include a means of storing mechanical energy in certain of its parts, such as a flywheel, sufficient to smooth out the action of the engine and carry it over the dead periods while the direction of motion of the piston is being reversed. Substantial improvement in the weight and complexity of the engine could be accomplished if these "dead periods" could be substantially reduced or eliminated.
External combustion reciprocating engines of this sort have a number of advantages, including high starting torque, wide speed range using manual control, suitability for slow rotative speeds, reversibility of direction of rotation, etc. However, these engines tend to be large and heavy in proportion to output power, and by highly complex and costly per unit capacity.
In converting from reciprocating piston motion to rotary output motion, most engines use a connecting rod connecting the piston to an eccentric crank pin on the output shaft. Conventional internal combustion engines use a wrist pin within the piston so that the connecting rod may move from side to side as the crank pin moves around the output shaft. However, in steam engines having power producing cylinder spaces on both sides of a wide, thin piston, the piston rod must be rigidly fastened to the piston and must move in a straight line through a packing gland. Thus, it is necessary to connect the piston rod to a cross-slide in a housing assuring straight line piston rod movement. A connecting rod then extends from a bearing pin on the cross-slide to the crank pin. This cross-slide and housing arrangement is cumbersome, heavy and expensive to manufacture but is ordinarily considered essential in these engines. Crank shafts on such engines are complex and expensive to manufacture, requiring extensive machining operations, yet do not provide for adjustments.
Thus, there is a continuing need for improved engines having reduced complexity and cost, coupled with higher energy efficiency.